This invention relates to apparatus for simulating the loads acting on the arms of an aircraft pilot under high G conditions and, more particularly, the invention is concerned with providing strategically positioned torque motors embedded within a flight suit to produce torque and thereby load the upper and lower arm of the pilot to simulate the effect of acceleration loading of primary consequences, +Gz.
It has been found that, in order to obtain useful G induced extremity loading stimuli, it is necessary to actually physically load the extremity in question. The acceleration effects operating on the upper arm are especially significant and lead to cross loading error wherein, in horizontal plane reaching movements in the presence of +Gz conditions, the hand falls short of its intended target. Thus, it can be seen that the mechanization of arm loading stimulti production requires equipment configured to exert force or load on the arm itself and the mechanization must allow load to be individually placed on the upper and lower arms.
Obviously the inherent high degree of arm mobility and the requirements to exercise this mobility in the course of piloting and operating the onboard system of a tactical aircraft severely constrain the arm loading concepts. It is not satisfactory to require that the arm be confined to a specific attitude or location in order to permit loading, rather the loader must "follow" arm motion operating when appropriate. Normally we would expect to find the upper arm in the neutral position which causes it to be approximately parallel to the spinal column. In reaching forward toward cockpit instruments or controls, shoulder flexion (elbow directed forward) up to 90.degree. can be expected and occassionally may be accompanied by some adduction (elbow directed transversely across the body) or abduction (elbow directed transversely away from the body). Shoulder joint forward elevation (elbow directed upwards above the horizontal plane) is much less likely to occur in tactical aircraft due to the absense of controls above shoulder height.
Under high G conditions the mass of the upper arm, when in the neutral state, increases the load required to be suported by the shoulder joint and when in flexion, with or without adduction or abduction, increases not only load but the torque operating at the shoulder joint. The load is supported by the skeletal frame and torso muscular system governing this frame and is likely less noticable than the torque which affects the shoulder joint muscular system alone. Under worst case conditions wherein the arm is horizontally outstretched (zero degrees elbow flexion, 90.degree. shoulder flexion) and assuming a 5 pound upper arm mass operating 5.5 inches from the shoulder joint and a 5 pound lower arm mass operating 17.5 inches from the shoulder joint, the Gz induced shoulder torque amounts to approximately 9.5 ft-lb/G. As the upper arm is rotated downwards toward the neutral position, the effective mass moment arm becomes less and the torque diminishes.
Under normal cockpit conditions we could expect to find the lower arm in near 90.degree. flexion (parallel to the horizontal plane when the upper arm is in the neutral position) and may be rotated internally (transversely across the body) or in minor amounts externally (transversely away from the body). Maintaining lower arm at 90.degree. flexion and raising the upper arm from the neutral point to 90.degree. flexion causes the lower arm to be vertically oriented. This position as well as lower arm internal and external rotation from this position produce arm attitudes of a special nature which impose constraints affecting the design approach.
A typical reaching maneuver requires the upper arm to move in flexion various amounts from the neutral point toward 90.degree. flexion while relaxing the lower arm a commensurate amount from 90.degree. flexion toward zero degrees (arm horizontally extended forward from the shoulder). The lower arm is generally maintained somewhat parallel to the horizontal plane at the varied amounts of upper arm flexion. Under these conditions high G effects on the lower arm increase the load and torque. Considering the lower arm weight to be 5 pounds operating 6.5 inches from the elbow, 2.7 ft-lb/G of torque is experienced.
Initially it was felt that a suitable mechanization would employ thin long pneumatic bellows to drive an elbow hinge embedded within the flight suit and thus torque the lower arm with respect to the upper arm. This approach was abandoned due to the problems which arise in accounting for bellows spring rate force which is positionally dependent and would interact with subject movement of elbow flexion angle and unduly complicate the drive model. The characteristics of a torque motor in which torque or force, independent of position, is obtained is a much more suitable drive device. The recent introduction of samarium cobalt motors which display up to five times the torque of similarly sized Alnico motors makes a torque motor approach feasible. Suitable force can be generated by devices which are small enough to be contained on one's person.